The recruitment of monocytes to areas of acute inflammation is a later stage in the inflammatory process. We have previously shown that systemic inhibition of either p38 or c-Jun NH2-terminal kinase (JNK) limits neutrophil recruitment to the lung in an LPS-induced model of acute inflammation. As we will show, however, inhibition of JNK, but not p38, limits the pulmonary recruitment of monocytes, which occurs through monocyte chemoattractant protein 1 (MCP-1) and neutrophil dependent pathways. Understanding mechanisms that lead to JNK activation in neutrophils will, therefore, be fundamental to the understanding of monocyte recruitment. While activation of p38 in neutrophils occurs in suspended conditions, activation of JNK requires neutrophils to be cultured in adherent conditions, although the cell surface proteins that regulate cell adhesion, and thereby JNK activation, are poorly understood. One such family, the syndecans, bind to the extracellular matrix (ECM) inducing cell adhesion. In addition, syndecan-4 has been shown to co-associate with CXCR4, and we will show here with the IL-8 receptor CXCR2 in neutrophils. We propose to examine the role of syndecan-4 in regulating IL-8-induced JNK activation in neutrophils, and thereby expression of MCP-1, by examining if syndecan-4 enhances JNK activation via an upregulation of protein kinase C alpha (PKC() activity, examine mechanisms for the co-association of syndecan-4 with CXCR2, and the necessity of the co-association for the enhancement of IL-8-induced JNK activation. We will use several techniques including chemical inhibitors, blocking antibodies, small interfering RNAs, and protein transduction of neutrophils and the PLB-985 cell line, which can be differentiated into neutrophil-like cells. In addition, to confirm our findings from neutrophils and PLB-985 cells, we will utilize neutrophils derived from syndecan-4, CXCR2, and PKC( deficient mice. Utilizing the above techniques we will examine components that we hypothesize to regulate syndecan-4-induced PKC( and JNK activation, including PKC-( and PP2A, or to regulate the co-association of syndecan-4 with CXCR2, including the adaptor proteins CASK and syntenin. These studies will provide vital insights into mechanisms that regulate JNK activation in neutrophils and will suggest roles for novel pathways in the regulation of lung inflammation, and in particular pulmonary monocyte recruitment.